You can use the audio out from your tablet but it is only two channel. You would have to feed it to a crossover to get your subwoofer output or use some other sort of processor.
Your tablet should have bluetooth out and you could use that but would be the less desirable solution.
Otherwise if you want to go off your USB you can look for just about any USB sound card. The only issue will be if your ROM recognizes your sound. You MAY also be able to find a DAC that will work as well but I have no experience with a DAC and android. A DAC will have built in crossovers and in some cases time alignment stuff but I have not heard of a DAC that works with Android.